Calculating NS Index linked saving certificate values

cepheus

When calculating your interest NS&I use the RPI figure from two months before your interest is due. For example if you are due your annual interest payment in March the January RPI figure, which would be announced in February is used.

http://www.ons.gov.uk/ons/rel/cpi/consumer-price-indices/january-2014/stb---consumer-price-indices---january-2014.html#tab-Retail-Prices-Index--RPI--and-RPIJ-

So the RPI part should be fixed for twelve months until each anniversary, using the RPI two months before the start and end dates in each case, whilst the added % part is added on every month?

I can get figures very close that way but not exact.

Stompa

cepheus wrote: »

I can get figures very close that way but not exact.

My calculations have always been a bit out too. But have you tried looking at their own spreadsheet, which is linked to here:

http://www.nsandi.com/savings-index-linked-savings-certificates-calculator

cepheus

Yes that's why I know I'm out, but their calculations (equations) aren't shown.

Stompa

There's something odd going on with their calculator. In the other thread a week ago I wrote "For me today it seems to be showing values that are around 1% lower than the values it gave me a week ago."

http://forums.moneysavingexpert.com/showpost.php?p=64805841&postcount=68

Today the values it's giving me are around 20% lower! It doesn't make any sense.

FWIW somebody else seems to have spotted this too:

http://boards.thisismoney.co.uk/savings-investing-pensions/34031-ns-i-index-linked-calculation-error.html

talexuser

Just checked again, my total has increased £225 since yesterday! same dates.

If I increase my start day by 1, ie from the 11th to the 12th of the month, the £225 disappears again.

Stompa

talexuser wrote: »

Just checked again, my total has increased £225 since yesterday! same dates.

Hey that's not fair, mine has dropped by £246!

cepheus

Actually this sounds more exciting, perhaps they are competing with the National Lottery?

talexuser

Last week I sent a message on the contact page asking why the totals were moving around, no reply yet.

Maybe if all of us did the same it would hurry things up a bit? Even ask for their formulas - there is a link to their statistician.

http://www.ons.gov.uk/ons/rel/cpi/consumer-price-indices/january-2014/stb---consumer-price-indices---january-2014.html#tab-statistical-contacts

I know it's kind of funny at the moment, but this is OUR interest we are talking about and we need have some confidence they know what they are doing here.

cepheus

Sent them a Mail!

Lansdowne

Talexuser, that link is to the ONS, not to NS&I. The ONS (Office of National Statistics) publishes the index values, but is not in any way responsible for the calculations of NS&I certificate values.

Actually Cepheus, you may have a point that the values do not move to the next RPI value on the first of the month, but on the "monthiversary" as someone called it. I will check the conditions for the new-style certs.